This invention relates to a circuit configuration that, when implemented into an antenna power distribution network, provides independent sum and difference aperture excitations. This enables a reduction in the difference channel radiation pattern sidelobe levels with insignificant degradation on the sum channel radiation pattern.
In general, there are two types of constrained feed networks for antenna array systems: traveling wave and corporate feeds. They are distinguished by the method by which they distribute RF energy. In a travelling wave type, RF energy is inputted into a main transmission line and as it traverses the length of this line, small amounts are coupled off into the output ports of the feed. The path lengths from the input point to every feed output port are different. In contrast, in a corporate feed the inputted RF energy is continuously divided into smaller amounts eventually reaching the output ports. In this case, the path lengths from the feed input point to every output port are identical. A travelling wave feed can be designed to have equal path lengths from the feed input point to each output port, but this approach adds hardware complexity.
Conventional power distribution networks for antenna arrays provide control only of the sum channel radiation pattern sidelobes. Low sidelobe sum pattern designs invariably exhibit difference patterns with poor (high) or indiscernible sidelobe structure.
Several power distribution network schemes have heretofore been developed that allow independent control of the aperture excitation by the sum and difference channels. Most of these schemes are very complex and difficult to implement into hardware. In addition, networks that provide independent sum and differences channel aperture excitation are constrained to "series" or traveling wave types of circuits. This restriction makes such networks attractive to only narrow instantaneous bandwidth applications. These "traveling wave" feed configurations and the conventional independent aperture control scheme can be converted to "parallel" or "equal path length" structures with wide instantaneous bandwidth characteristics. However, this conversion is very unattractive for large array systems because of packaging complexity, weight and cost.
It would therefore represent an advance in the art to provide an independent aperture excitation network which is applicable to both parallel and series feeding structures and is simple in its hardware implementation.
It would further be advantageous to provide a relatively low cost and simple (in hardware) approach to the reduction of difference pattern sidelobes without any impact on the sum pattern sidelobes.